With the advent of convenience copiers adapted to produce copies of a number of different sized originals, the need was recognized for interchangeable copy paper cassettes designed for rapid and simple insertion into the copier, the cassettes being adapted to accept the sizes of copy paper normally encountered, such as 8 1/2 .times. 11, 8 1/2 .times. 13, and 8 1/2 .times. 14, to enable rapid changeover of the machine to produce the desired size copies.
In providing a cassette for a convenience copier, a number of problems must be addressed. First the cassette must be rapidly and easily removable and insertable. Further, upon insertion, means must be provided to accurately position the cassette within the machine to enable proper operation of the sheet separator associated therewith. A mechanism must also be provided to assure that the cassette is securely locked in the machine. Once the copying operation begins, in a top feeder, means must be provided to maintain the top sheet in the stack in contact with the sheet feeder either by raising the sheets in the cassette into contact with the feeder, or by allowing the feeder to drop into the cassette or "eat its way" into the paper stack as the sheets are depleted.
In recent years, friction retard feeders having a feed belt in contact with the sheet to be fed, adapted to feed sheets from the stack through a retard throat formed by a portion of the feed belt and a stationary retard pad to prevent multiple sheet feeding has found increased acceptance. With this type of feeder, ordinarily the second sheet, or the sheet adjacent to the sheet being fed, is dragged partially into the nip formed by the feed belt and the retard pad. When this type of feeder is utilized with a cassette type paper tray, after the copy opertion is completed and the cassette is removed from the machine either to replenish the paper supply or to replace the cassette with a cassette containing different sized sheets, the sheet which has been dragged into the nip of the feeder may be held in the machine and be pulled out of the cassette as the cassette is removed. Thus, the operator must reach into the machine and remove this sheet prior to reinsertion of a cassette, or if this sheet is not completely pulled out of the cassette, the sheet must be carefully fed back into the cassette before the cassette can be reinserted.
Another problem encountered with friction retard feeders is rapid wear of the friction retard pad since each sheet of paper fed from the machine is dragged across this pad.
It is therefore an object of the present invention to provide an improved copy sheet cassette for use in a convenience copier wherein the friction retard pad is mounted within the cassette, thereby maintaining all of the sheets within the confines of the cassette, even those which are dragged into the nip between the feed rolls and the retard pad to prevent retention of sheets in the machine upon the removal of the cassette. It is the further object of this invention to provide a cassette adapted for secure and accurate location within a convenience copier and which is provided with means for holding the top sheet in the stack against the feed mechanism to provide the required normal force therebetween for optimum sheet feeding.